/*
 * Copyright (c) 2013, SRI International
 * All rights reserved.
 * Licensed under the The BSD 3-Clause License;
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at:
 * 
 * http://opensource.org/licenses/BSD-3-Clause
 * 
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 
 * Redistributions of source code must retain the above copyright
 * notice, this list of conditions and the following disclaimer.
 * 
 * Redistributions in binary form must reproduce the above copyright
 * notice, this list of conditions and the following disclaimer in the
 * documentation and/or other materials provided with the distribution.
 * 
 * Neither the name of the aic-expresso nor the names of its
 * contributors may be used to endorse or promote products derived from
 * this software without specific prior written permission.
 * 
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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package com.sri.ai.grinder.library.number;

import com.google.common.annotations.Beta;
import com.sri.ai.expresso.api.Expression;
import com.sri.ai.expresso.core.DefaultSymbol;
import com.sri.ai.expresso.helper.Expressions;
import com.sri.ai.grinder.api.RewritingProcess;
import com.sri.ai.grinder.core.AbstractRewriter;
import com.sri.ai.grinder.library.FunctorConstants;
import com.sri.ai.util.math.Rational;

/**
 * Implements a rewriter for the minus operation.
 * 
 * @author braz
 *
 */
@Beta
public class Minus extends AbstractRewriter {
	public static String FUNCTOR = FunctorConstants.MINUS;

	@Override
	public Expression rewriteAfterBookkeeping(Expression expression, RewritingProcess process) {
		Expression result = expression;
		if (expression.hasFunctor(FUNCTOR) && expression.numberOfArguments() == 2) {
			Expression first = expression.get(0);
			Expression second = expression.get(1);

			if (Expressions.isNumber(first)) {
				Rational firstValue = first.rationalValue();
				if (Expressions.isNumber(second)) {
					Rational secondValue = second.rationalValue();
					result = DefaultSymbol.createSymbol(firstValue.subtract(secondValue));
				} 
				else if (firstValue.isZero()) {
					result = Expressions.apply("-", second);
				}
			} 
			else if (Expressions.isNumber(second) && second.rationalValue().isZero()) {
				result = first;
			}
		}
		
		return result;
	}
	
	public static Expression make(Expression e1, Expression e2) {
		return Expressions.apply(FUNCTOR, e1, e2);
	}	
}
